The speed of sound

We usually hear sounds made by air moving, but sound can travel through any material. When sound travels through materials (like air), the molecules move back and forth. When an object vibrates, the air molecules around the object travel out in waves in all directions from the object (like the ripples made from a pebble dropped in a pond).

The speed at which sound moves depends on the material through which sound waves travel. Sound travels faster through liquids and solids than through gases because the molecules in liquids and solids are closer together. In air, the speed of sound varies depending on such things as altitude, density, and temperature. In normal air at room temperature, the speed of sound is 758 miles per hour (1220 kilometers per hour). When an object travels at the speed of sound, this speed is known as Mach 1.

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